Chapter 15

Water Quality for Irrigating Vineyards

Water Hardness

The term hardness refers to the combined concentration of calcium and magnesium in the water and is expressed as the total amount of calcium carbonate (CaCO3) in milligrams per liter of water (mg/L). Other cations such as iron, manganese, aluminum and zinc can also contribute to hardness. Hardness can be used as an indicator of alkalinity. The amounts of these two elements in irrigation water are variable. For example, ground water from a limestone aquifer may contain more than 100 ppm calcium, while water from a granite or sandstone aquifer may contain less than 10 ppm calcium.

Limescale Potential

Hard water tends to precipitate calcium carbonate, commonly referred to as limescale or lime. Lime deposition from irrigation water occurs because environmental factors such as evaporation of water, loss of carbon dioxide as a gas, increased temperature, and increased pH act to reduce the solubility of lime in water. Scale formation in vineyard irrigation systems is a chronic problem. That is, it slowly builds up over time, gradually restricting the flow through pipes and emitters.

Removing Lime from Water

Lime residues can be minimized by lowering water pH to below 6.5. Lowering pH is accomplished by injecting acid or by using a sulfur burner to generate acidifying sulfur compounds. Lime deposition potential is reduced as bicarbonate is converted to carbon dioxide. When sulfuric acid is used, calcium carbonate/bicarbonate (lime) in the water is converted to calcium sulfate (gypsum).

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